The ciliary ganglion is a peripheral parasympathetic ganglion which innervates muscular structures of the eye. Through regulation of pupillary size, it exerts important effects on the physiological processes of accommodation, convergence and visual acuity and may be an important factor in the development of myopia and treatment of glaucoma. Knowlege about the ionic mechanisms which generate electrical activity in the neurones of the ciliary ganglion will further understanding of physiological and pathological processes of the eye as well as of the parasympathetic nervous system in general. Conventional microelectrode studies have shown that K+ channel blockers significantly alter the electrical activity of chick ciliary ganglion neurones, suggesting that K+ channels play an important role in generating or regulating the intrinsic activity of these cells. Preliminary path clamp studies have identified three operationally distinct K+-selective ion-channels, which differ in conductance and gating properties, in the membrane of cultured chick ciliary neurones. The proposed project seeks to continue extracellular patch clamp studies of single K+ currents in cultured chick ciliary neurones. The aim will be to characterize the three K+ channel populations and identify the factors (voltage, ions, time, chemicals, and neurotransmitters) which regulate their activity. Specifically biophysical properties, including single ion-channel conductance, ionic selectivity, voltage- and Ca2+-sensitivity, gating kinetics, and sensitivity to conventional K+ channel blockers will be determined and compared for each K+-selective channel. Modulation of the various channel properties by nonclassical transmitters, including amines, amino acids, and peptides, will be examined. In addition to the cited relevance to physiology of the eye and to the parasympathetic nervous system, this project may suggest further studies to elucidate the role that neurotransmitters play in multiple input chemical signalling.